1. Field of the Invention
The invention relates to a method for traction control in a motor vehicle in accordance and to a control system for carrying out the method.
2. Description of the Related Art
Traction control at driven wheels or axles of a motor vehicle is well known. Thus, a wheel slip is understood to mean the ratio of the speed of a wheel center point of the wheel to the circumferential speed of the wheel. There is no slip when the wheel center point speed of the wheel corresponds to the circumferential speed of the wheel.
Drive traction control refers to carrying out traction control in the traction mode of the motor vehicle.
Motor overrun control refers to carrying out traction control in the overrun mode or braking mode of the motor vehicle.
Traction control uses an ESP control unit to determine a setpoint slip that is dependent on the driving situation for the driven axles or the driven wheels of the motor vehicle in a manner that is dependent on the current driving situation, and determines a setpoint circumferential speed for the driven wheels from the setpoint slip.
The setpoint circumferential speed for the wheels is compared in the ESP control unit with an actual circumferential speed that has been detected using measuring technology, in order thus to influence the drive moment of the drive unit of the motor vehicle on the basis of a control deviation between the actual slip and the setpoint slip. For this purpose, the ESP control unit determines permissible limit values for the drive moment of the drive unit and provides the limit values to a motor control unit. The motor control unit limits a driver-side desired drive moment on the basis of the limit values.
Traction control that controls the drive moment of the drive unit in a manner that is dependent on the control deviation between the setpoint slip and the actual slip is suitable for motor vehicles that have an internal combustion engine as the drive unit. Hybrid vehicles and pure electric vehicles have a drive unit that comprises at least one electric machine. The control of the drive moment on the basis of the control deviation between the setpoint slip and the actual slip is disadvantageous in vehicles that have a drive unit with at least one electric machine. More particularly, the drive moment in electric machines is very dynamic in comparison with internal combustion engines, and, as a result, oscillations disadvantageously can be caused in the traction control.
US 2010/0286858 discloses a control system for a hybrid vehicle, in which traction control takes place by way of influencing the drive moment of the electric machine of the hybrid drive.
It is an object of the invention to provide an improved method for traction control in a motor vehicle and a control system for carrying out the method.